1. Field of the Invention
This invention relates to an image forming apparatus to which electrophotography is applied and in which developing devices are used, switched from one to anther.
2. Description of the Related Art
Generally, an image forming apparatus to which electrophotography is applied have a photosensitive member, a charging device, an exposing device, a developing device, a transfer device and a fixing device. The photosensitive member may have an electrically charged area. This area is electrically discharged when light is applied to the photosensitive member. The charging device charges the photosensitive member. As the exposing device applies light to the photosensitive member, an electrostatic latent image is formed on the photosensitive member. As the developing device makes the electrostatic latent image attract toner, a visible toner image is formed on the surface of the photosensitive member. The transfer device transfers the toner image from the surface of the photosensitive member onto a recording sheet. The fixing device fixes the toner image that the transfer device has transferred onto the recording sheet.
Multi-color image forming apparatus have a developing device assembly that comprises a plurality of developing devices. The assembly is a means for forming multi-color images. Each developing device has a toner container. The toner containers store toners of different colors. In the multi-color image forming apparatus, the developing device assembly is rotated like a cylinder of a revolver to one developing device to another. The multi-color image forming apparatus forms a multi-color image on the surface of a recording sheet by repeating the image forming routine at the photosensitive drum, for the respective developing devices. Note that the image forming routine is a sequence of charging, exposing, developing and transferring. Since the image forming procedure is repeated as many times as the number of the developing devices, the multi-color image forming apparatus needs more time to form a complete image than the mono-color image forming apparatus.
Recently, there is a strong demand for multi-color image forming apparatus that can form images at high speed. One of the methods devised to meet the demand is to operate each device at high speed.
The developing device assembly is rotated intermittingly to switch one developing device to the next one. Each time the assembly starts or stops rotating, it vibrates due to its own moment of inertia. The vibration affects the image forming operation of the multi-color image forming apparatus.
If the exposing device vibrates, the light beam irradiating the surface of the photosensitive member may miss the target. If the developing device assembly vibrates, the distance between the developing device and the photosensitive member will change incessantly. The toner will be attracted, inevitably in uneven density, to the surface of the photosensitive member due to the electrostatic force. The faster the developing device assembly rotates, the greater the kinetic energy of the developing device assembly. Consequently, the vibration of the developing device assembly increases.
The vibrations of the devices result in misregistration of the color layers laid one on another. In order to avoid misregistration of colors, each device needs to wait until it ceases to vibrate, before it starts operating.
An image forming apparatus according to an embodiment of the present invention is designed to reduce the vibration that occurs in each stop after switching one developing device to another in the developing device assembly that comprises a plurality of developing devices.
An image forming apparatus according to an aspect of the present invention comprises a developing device assembly, an inertia acceptor and a setting mechanism. The developing device assembly has a plurality of developing devices for developing a latent image formed on a photosensitive member. The assembly can rotate to switch one developing device to the next one. The energy of rotational inertia is shifted from the developing device assembly to the inertia acceptor, in order to stop the rotation of the developing device assembly. The setting mechanism controls the movement of the inertia acceptor that has received the energy of the rotational inertia from the developing device assembly.
An image forming apparatus according to another embodiments comprises a developing device assembly and an inertia acceptor. The developing device assembly has a plurality of developing devices for developing a latent image formed on a photosensitive member. The assembly can rotate to switch one developing device to the next one. The inertia acceptor shifts the energy of rotational inertia to the developing device assembly to make the assembly start rotating, and is shifted the energy of rotational inertia from the developing device assembly in order to stop the rotation of the developing device assembly.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.